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Space Tether for Payload Orbital Transfer
Published in Yi Chen, Yun Li, Computational Intelligence Assisted Design, 2018
As shown in Figure 14.1 [Chen(2010a), Logsdon(1997), Curtis (2004), Roy and Clarke (2003)], the geocentric inertial coordinate system is utilized in space tether dynamical modeling, in which the nodes are the points where an orbit crosses on orbital plane and the space tethers are crossing the Earth’s equatorial plane. Space tether system dynamics are quite complex because they are governed by a set of ordinary or partial non‐linear equations and coupled differential equations, various aspects of which can affect the space tether system behavior and can cause control problems, which could be coupled with other problems. Momentum exchange (MX) tethers and Electrodynamic (ED) tethers are the two principal categories of practical tether systems. There are many types of tether applications, such as Hybrid of Momentum exchange/Electrodynamic Reboost (MXER) tethers, as given in Figure 14.2, and Electrostatic tethers. The research on dynamics and control represents the two fundamentally important aspects of all tether concepts, designs and mission architectures.
Horizontal path-following control for deep-sea work-class ROVs based on a fuzzy logic system
Published in Ships and Offshore Structures, 2018
Xingxing Huo, Tong Ge, Xuyang Wang
The functions of the umbilical cable are to supply electricity to the ROV and to transfer data between the ROV and the tether management system (see Figure 3). The umbilical cable force is mainly generated by the relative motion between the umbilical cable and seawater. However, the relative motion between the large part of the umbilical cable and the seawater is relatively small, because the working depth of the deep-sea work-class ROV is large and the umbilical cable is very long. Therefore, the umbilical cable force is small and is mainly generated by a very small part of the umbilical cable near the ROV. It can be assumed that the magnitude of the force generated by the small part of the umbilical cable is proportional to the second-order relative velocity, the direction of the force is opposite to the relative velocity and the speed of the small part of the umbilical cable is approximate to the speed of the ROV. In addition, the moment about the vertical axis from the umbilical cable is zero, because the umbilical cable is linked to the vertical axis of the ROV. Hence, the simplified model of the umbilical cable can be written as where Kx and Ky are the coefficients of the cable disturbing forces.
Assessing tether anchor labeling and usability in pickup trucks
Published in Traffic Injury Prevention, 2018
Kathleen D. Klinich, Miriam A. Manary, Laura A. Malik, Carol A. Flannagan, Jessica S. Jermakian
FMVSS No. 225 specifies a zone for tether anchor placement. If a tether anchor is outside the allowable tether zone, then a tether router located in the zone can be used to redirect the tether to a tether anchor. Tether routers are commonly used in pickup trucks because of space constraints. In configurations with tether routers, the router (usually a loop made of webbing or plastic coated wire) often serves 2 roles: the tether hardware immediately behind the installation seat position serves as a router, and the hardware in the adjacent seat position serves as the tether anchor. In a survey of 2010–2011 vehicles, 2 of 10 pickup trucks used a tether router configuration with the tether anchor located in an adjacent seating position or other lateral location (Klinich, Flannagan, et al. 2014). In IIHS's LATCH ratings of 2016 pickups, 9 of 10 pickups used a tether router to reroute the tether to an anchor in an adjacent seat position.